Microwave chip supporting structure

ABSTRACT

The present invention relates to a microwave chip supporting structure comprising a first microwave laminate layer, with a first side and a second side, and an outer limit. At least one conductor is formed on said first side extending towards said outer limit. The microwave chip supporting structure further comprises a second microwave laminate layer, with a first side and a second side, the second side of the second laminate layer being fixed to at least a part of the first side of the first laminate layer. The first laminate layer and/or the second laminate layer comprises at least one recess arranged for receiving a microwave chip intended to be connected to said conductor. The second laminate layer extends outside the outer limit of the first laminate layer, said conductors continuing on the second side of the second laminate layer without contacting the first laminate layer.

TECHNICAL FIELD

The present invention relates to a microwave chip supporting structurecomprising a first microwave laminate layer, with a first side and asecond side, the first microwave laminate layer having an outer limit,where further at least one conductor is formed on the first side of thefirst laminate layer, said conductor extending towards the outer limitof the first laminate layer.

BACKGROUND

In microwave technology, it has become technically feasible to integratecircuits in commercial packages for volume manufacturing and sale.Previously it was necessary to design a layout and mount discretecomponents on that layout, where a matching procedure often wasnecessary afterwards in order to tune the circuit. These packagedintegrated microwave circuits thus make microwave design easier andcheaper than before.

A number of such packages have been developed during the last years. Apackage normally comprises a circuit with etched components on a siliconsubstrate, constituting a microwave chip. A package normally furthercomprises a carrier, for example in the form of a microwave laminate, towhich the chip is fixed. The chip comprises connecting points, which areconnected to connecting points on the laminate by means of bonding,using very thin gold wires. The laminate communicates its connectingpoints via a plurality of connectors, accessible for a user. Thelaminate and its chip are normally provided with a protective covering,for example an epoxy resin, a plastic cover shell, or both.

One such type of package is the so-called BGA (Ball Grid Array) package,which is an encapsulated circuit with a more or less complete M×N arrayof connectors on its lower side, constituting a so-called footprint. Theconnectors are in the form of balls which stands out a certain distancefrom the package. A circuit board on which the package is to be mountedhas a corresponding soldering pattern comprising corresponding solderingpads, matching the footprint—one pad for each ball-shaped connector onthe package. An adhesive soldering paste is dispensed on each pad. Thepackage is placed on the circuit board in such a way that theball-shaped connectors contact the desired corresponding soldering pads.Then the circuit board is gently heated in such a way that the balls andthe soldering paste melts, followed by cooling, where the pads and theconnectors now are soldered together.

The solder joint more or less preserves its spherical shape, creating astand-off between the package and the circuit board. This is, however,disadvantageous at higher frequencies, since this stand-off constitutesan inductance which is difficult to predict with sufficient accuracy.

Another type of package is called QFN (Quad Flat No lead) which isrectangular with connectors arranged at all four sides. The connectorsdo not extend out from the outline of the package, but extend at leastpartly along the lower side of the package. The chip is glued to alaminate, and its connecting points are connected to connecting pointson the laminate by means of bonding, using very thin gold wires. Theconnecting points on the laminate are in turn connected to theconnectors of the package by means of via holes that extend from the topof the laminate where its bond-connected connecting point is positioned,to the lower side of the laminate, where the connector is positioned.

This configuration is, however, disadvantageous since there are twoinductances present for each connection; the bond wire and the via. Thehigher frequency, the more problematic do these inductances become fordesigning an accurate, repeatable construction.

One other type of package is called flip-chip, and comprises a chip ofBGA type, but much more miniaturized. The chip is soldered as anordinary BGA package to a laminate in order to constitute either a BGApackage or a QFN package.

If it is a BGA package, there are problems with stand-off distances forthe ball connectors at the chip as well as at the lower side of thelaminate. There are also vias connecting between connecting points onthe upper side of the laminate, and the ball connectors on the lowerside of the laminate.

If it is a QFN package, there are problems with stand-off distances forthe ball connectors at the chip and those vias connecting betweenconnecting points on the upper side of the laminate, and the connectorson the lower side of the laminate.

As described in U.S. Pat. No. 6,011,692, which is considered as closestprior art, a chip is bonded to connectors at a supporting element intowhich the chip is fastened. The bottom of the chip rests on a conductivefoil. The supporting element is lowered into a recess in a circuit boardwith a ground plane. In the recess, the dielectrica of the circuit boardis completely removed, allowing the lowered supporting element to reston the conducting foil constituting the ground plane of the circuitboard. In this way, the ground of the chip is easily connected to thecircuit board ground. The connectors of the supporting element areconnected to conductors at the circuit board via conductors, soldered orglued in place.

Although the known device functions in a satisfactory manner, there arecertain aspects which can be improved, for example:

-   -   A glue or solder has to be applied to the conductors on the        supporting structure, and may interfere with the chip and/or        bond wires.    -   The transmission lines are broken by solder or glue joints at        two places after the bond wires    -   When mounting the supporting structure with its chip, the        circuit board has to be brought through two runs in a        pick-n-place machine and solder dispenser.    -   The bond wires are unprotected if no lid is positioned over the        supporting structure    -   Should a lid be placed over the supporting structure, the lid        will be in contact with the conductors

SUMMARY

It is an aim of the present invention to present a microwave chipsupporting structure adapted for microwave frequencies, which microwavepackage overcomes the above disadvantages.

This aim is achieved by means of a microwave chip supporting structureas mentioned in the introduction, where furthermore the microwave chipsupporting structure comprises a second microwave laminate layer, with afirst side and a second side, the second laminate layer being fixed tothe first laminate layer in such a way that the second side of thesecond laminate layer faces at least a part of the first side of thefirst laminate layer. The first laminate layer and/or the secondlaminate layer comprises at least one recess arranged for receiving amicrowave chip intended to be connected to said conductor. The secondlaminate layer further extends outside the outer limit of the firstlaminate layer, said conductors continuing on the second side of thesecond laminate layer without contacting the first laminate layer.

Preferred embodiments are disclosed in the dependent claims.

Several advantages are achieved by means of the present invention, forexample:

-   -   no glue or solder has to be applied to the conductors on the        supporting structure,    -   the transmission lines are unbroken, and    -   only one run in a pick-n-place machine and solder dispenser is        necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described more in detail withreference to the appended drawing, where

FIG. 1 shows a top view of a first embodiment of the present invention;

FIG. 2 shows a section of the first embodiment of the present invention;

FIG. 3 shows a section of the first embodiment of the present invention;

FIG. 4 shows a section of a variety of the first embodiment of thepresent invention;

FIG. 5 shows a section of a second embodiment of the present invention;

FIG. 6 shows a top view of a third embodiment of the present invention;

FIG. 7 shows a section of the third embodiment of the present invention;and

FIG. 8 shows a section of a fourth embodiment of the present invention.

DETAILED DESCRIPTION

In FIG. 1 and FIG. 2, illustrating a first embodiment, a microwave chipsupporting structure 1 is shown. Said supporting structure 1 comprises afirst microwave laminate layer 2, for example a PTFE-based laminate,with a first side 3 and a second side 4, where a copper ground plane 5is fixed to the second side 4. The first laminate layer 2 is limited bya first edge 6, a second edge 7, a third edge 8 and a fourth edge 9, thefirst laminate layer 2 being essentially rectangular. A first recess 10is formed in the first laminate layer 2, where the first recess 10 isformed in such a way that a part of the copper ground plane 5 is formingan accessible surface, against which a microwave chip 11 is fixed bymeans of, for example, soldering or gluing. Such a chip 11 is normallyconstituted by a circuit with etched components on a silicon substrate.The chip 11 has a top side 12 and a bottom side 13, the bottom side 13facing the ground plane. In that way, the chip's ground may be directlyconnected to the ground plane 5, since the chip's bottom side 13 has atleast one ground connection 14. The chip 11 and the microwave chipsupporting structure 1 together form a microwave package.

The chip 11 has connections 15, 16, 17, 18, 19, 20 on its top side 12,which connections 15, 16, 17, 18, 19, 20 are brought into contact withconductors 21, 22, 23, 24, 25, 26 formed on the first side 3 of thefirst laminate layer 2 by means of corresponding bonding wires 27, 28,29, 30, 31, 32. The conductors 21, 22, 23, 24, 25, 26 extend towards thefour edges 6, 7, 8, 9 of the first laminate layer 2.

According to the present invention, the supporting structure 1 furthercomprises a second microwave laminate layer 33, for example a PTFE-basedlaminate, with a first side 34 and a second side 35. The second laminatelayer 33 is fixed to the first laminate layer 2 in such a way that thesecond side 35 of the second laminate layer 33 faces the first side 3 ofthe first laminate layer 2. The conductors 21, 22, 23, 24, 25, 26 arethus positioned between the first laminate layer 2 and the secondlaminate layer 33. A second recess 36 is formed in the second laminatelayer 33, having essentially the same position as the first recess 10,but being larger in order to allow the bond wires 27, 28, 29, 30, 31, 32to be connected to the conductors 21, 22, 23, 24, 25, 26.

The second laminate layer 33 further extends outside the four edges 6,7, 8, 9 of the first laminate 2, the conductors 21, 22, 23, 24, 25, 26continuing out from the first laminate layer 2 and continuing on thesecond side 35 of the second laminate layer 33. The second laminate 33layer thus carries the conductors 21, 22, 23, 24, 25, 26 out from thefirst laminate layer 2.

As shown in FIG. 3, a first PCB (printed circuit board) 37 and a secondPCB 38 is shown. The first PCB 37 has a first side 39 and a second side40, and the second PCB 38 has a first side 41 and a second side 42. Thefirst PCB 37 and the second PCB 38 are attached to each other in such away that the second side 40 of the first PCB 37 and the first side 41 ofthe second PCB 41 face each other with a PCB ground plane 43 positionedbetween. In the first PCB 37, a third recess 44 is formed in such a waythat a part of the PCB ground plane 43 is forming an accessible surface,against which the supporting structure 1 is fixed by means of, forexample, soldering or gluing.

The first PCB 37 has a thickness that essentially is the same as thethickness of the first laminate layer 2, resulting in that theconductors 21, 22, 23, 24, 25, 26, when carried only by the secondlaminate 33, will rest on corresponding PCB conductors 45, 46. Theconnections between the conductors 21, 22, 23, 24, 25, 26 on the secondlaminate 33 and the PCB conductors 45, 46 are achieved by means of forexample soldering or gluing.

In this way, each conducting path is only broken by one solder or gluejoint after the respective bond wire 27, 28, 29, 30, 31, 32.

The chip 11 is now surrounded by the second laminate layer 33, whichoffers a protection for the chip 11. In order to achieve a more rigidprotection of the chip, the second recess 36, formed in the secondlaminate layer 33, may be filled with a protective filler substance 47,such as for example epoxy. Other examples of the protective fillersubstance 47 are a gel or a silicone compound.

According to a variety of the first embodiment, as shown in FIG. 4, acover 48 is placed on the first side 34 of the second laminate layer 33,covering the chip 11 without interfering with any conductors 23, 26. Thecover 48 may for example be made in plastic, metal or a combination ofboth. The cover 48 may of course be combined with a protective fillersubstance as disclosed with reference to FIG. 3. The shape of the cover48 may vary, it may for example be arched or be constituted by a flatlid lying directly on the first side 34 of the second microwave laminatelayer 33.

According to a second embodiment of the present invention, withreference to FIG. 5, showing a microwave chip supporting structure 1′,the second laminate layer 33′ is not provided with a recess, but coversthe chip 11. In this second embodiment, there are no bond wires, but thesecond laminate layer 33′ carries the conductors 23, 26 partly into thefirst recess 10, enabling them to achieve a direct contact with the chipconnections 17, 20, thus dispensing with the need for bond wires. Inthis way, the second laminate layer functions as:

-   -   a first connecting means, between the chip connections and the        conductors on the first side of the first laminate,    -   a second connecting means, between the conductors on the first        side of the first laminate and the PCB connections, and    -   a cover for the chip.

The second embodiment corresponds to the first embodiment regarding allother features, and may of course be attached to a PCB in the same wayas described for the first embodiment.

In FIG. 6 and FIG. 7, illustrating a third embodiment, a microwave chipsupporting structure 1″ is shown. Said supporting structure 1″ comprisesa first microwave laminate layer 49, for example a PTFE-based laminate,with a first side 50 and a second side 51, where a copper ground plane52 is fixed to the second side 51. The first laminate layer 49 islimited by a first edge 53, a second edge 54, a third edge 55 and afourth edge 56, the first laminate layer 49 being essentiallyrectangular.

The supporting structure 1″ further comprises a second microwavelaminate layer 57, for example a PTFE-based laminate, with a first side58 and a second side 59. The second laminate layer 57 is fixed to thefirst laminate layer 49 in such a way that the second side 59 of thesecond laminate layer 57 faces the first side 50 of the first laminatelayer 49. Conductors 60, 61, 62, 63, 64, 65 are formed between the firstlaminate layer 49 and the second laminate layer 57 in a similar way asdescribed for the previous embodiments. The conductors 60, 61, 62, 63,64, 65 are of the type CPW (co-planar waveguide), i.e. the conductorsare surrounded by their corresponding ground plane G, separated from theground plane by a small gap, in a way well known to the person skilledin the art.

A recess 66 is formed in the second laminate layer 57, being of such aform that a microwave chip 67 fits in the recess 66, the chip 67 havinga top side 68 and a bottom side 69. The chip 67 is arranged to rest onthe first side 50 of the first laminate layer 49 in such a way thatconnections 70, 71, 72, 73, 74, 75 on the bottom side 69 of the chip 67are brought into contact with the conductors 60, 61, 62, 63, 64, 65formed on the first side 50 of the first laminate layer 49.

The connections between conductors 60, 61, 62, 63, 64, 65 and the chipconnections 70, 71, 72, 73, 74, 75 are in the form of ball connectors Bwhich stand out a certain distance from the package. An adhesivesoldering paste is dispensed on an appropriate spot at each conductor60, 61, 62, 63, 64, 65 before the chip 67 is fitted in place. Then thecircuit board is gently heated in such a way that the balls B and thesoldering paste melts, followed by cooling, where the conductors 60, 61,62, 63, 64, 65 and the chip connections 70, 71, 72, 73, 74, 75 now aresoldered together.

The second laminate layer 57 further extends outside the four edges 53,54, 55, 56 of the first laminate 49, the conductors 60, 61, 62, 63, 64,65 continuing out from the first laminate layer 49 and continuing on thesecond side 59 of the second laminate layer 57. The second laminate 57layer thus carries the conductors 60, 61, 62, 63, 64, 65 out from thefirst laminate layer 49 in the same way as described for the previousembodiments.

The supporting structure 1″ according to the third embodiment may thusbe attached to a PCB in the same way as described for the previousembodiments. The copper ground plane 52 may be used for soldering thesupporting structure 1″ to the appropriate PCB, but is not necessary forany electric functions. If the supporting structure 1″ is glued to theappropriate PCB instead, the copper ground plane 52 may be omitted.

The ball connectors B of the third embodiment may be exchanged with anytype of convenient connection means, for example gluing with conductingglue, the main idea of the third embodiment is to present a supportingstructure 1″ to which it is possible to connect a chip 67 having bothsignal and ground connections on the same side of the chip 67, in thiscase the bottom side 69, allowing it to be connected to CPW conductors.

The recess 66 may be filled with a protective filler substance and/orcovered with a protective cover as described for the first embodiment.

In FIG. 8, a fourth embodiment of a microwave chip supporting structure1″′ is shown. This embodiment resembles the embodiment of FIG. 5, wherethere are no bond wires, but here the first laminate layer 8 carries theconductors 23, 26 partly into the first recess 10, enabling them toachieve a direct contact with the chip connections 17, 20, thusdispensing with the need for bond wires, since the second laminate layer33 ends before the first recess 10, forming the second recess 36 in thesame way as for the first embodiment. This means that the conductors 23,26 partly are protruding over the first recess 10, not having anysupport of the first laminate layer 8.

The copper ground plane 52 is removed at the first recess 10, the firstrecess being accessible from the second side 51 of the first laminatelayer 8. The chip 11 is preferably inserted from this side. This meansthat the chip's ground connection 14 is electrically separated from thecopper ground plane 52 of the microwave chip supporting structure 1″′when not being mounted. The chip's ground connection 14 and the copperground plane 52 are electrically connected when the microwave chipsupporting structure 1″′ is mounted on a PCB structure (not shown inFIG. 8) as described for the first embodiment. The chip's groundconnection 14 and the copper ground plane 52 are then directly connectedto the PCB ground plane 43 by means of, for example, soldering.

For the fourth embodiment, the second recess 36, formed in the secondlaminate layer 33, may be filled with a protective filler substance asdescribed previously with reference to FIG. 3 (not shown in FIG. 8).

The invention is not limited to the embodiments described, but may varyfreely within the scope of the appended claims. For example, theconductors 21, 22, 23, 24, 25, 26; 60, 61, 62, 63, 64, 65 on the firstlaminate layer 2; 49 extend towards at least one of the edges 6, 7, 8,9; 53, 54, 55, 56 of the first laminate layer 2; 49. The second laminatelayer 33, 33′; 57 extends a certain distance outside the at least oneedge 6, 7, 8, 9; 53, 54, 55, 56 of the first laminate layer 2; 49, theconductors 21, 22, 23, 24, 25, 26; 60, 61, 62, 63, 64, 65 continuing outfrom the first laminate layer 2; 49 and continuing on the second side35; 59 of the second laminate layer 33, 33′; 57. The second laminatelayer 33, 33′; 57 preferably only extends outside those edges 6, 7, 8,9; 53, 54, 55, 56 of the first laminate layer 2; 49 towards which theconductors 21, 22, 23, 24, 25, 26; 60, 61, 62, 63, 64, 65 of the firstlaminate layer 2; 49 extend.

The number of conductors on the first laminate layer 2; 49 is at leastone.

The second laminate layer 33, 33′; 57 thus extends outside at least oneedge 6, 7, 8, 9; 53, 54, 55, 56 of the first laminate layer 2; 49. Thelength of the extension, or extensions, should be appropriate to fulfillits connecting function.

The widths of the conductors should be adapted to achieve optimalperformance, usually by adapting them to the characteristic impedance ofthe system. Such an adaptation must take into account whether theconductors run as microstrip, i.e. essentially on a supportingdielectric structure without any dielectrica on the other side, or asstripline, i.e. squeezed between two supporting structures. The same isvalid if the conductors run in a CPW configuration.

The materials may also be chosen conveniently depending on performanceand cost requirements, the materials mentioned herein are only mentionedas an example. The laminate layer may for example be formed usingceramics instead of PTFE. Furthermore, the copper ground planes may forexample be formed in any suitable conducting material, for example gold.

The ground planes may furthermore be omitted if suitable, for example ifother ground connections are available.

The shapes of the materials and the recesses may also vary in any way,the recess may be oval or circular, if that is more convenient due tomanufacturing or chip structure. The edges 6, 7, 8, 9; 53, 54, 55, 56may be arranged in any way, the function of the edges is to define anouter limit of the first laminate layer 2; 49.

The conductors on the PCB may be in the form of CPW for all embodiments.

1. A microwave chip supporting structure comprising: a first microwavelaminate layer having a first side and a second side, the firstmicrowave laminate layer having an outer limit where further at leastone conductor is formed on the first side of the first laminate layer,said conductor extending towards the outer limit of the first laminatelayer, wherein the first laminate layer has a first recess, into which amicrowave chip is inserted, the microwave chip having a top side and abottom side, the bottom side facing an electrically conducting groundplane that is fixed to the second side of the first laminate layer, andthe top side being equipped with chip connections, which the chipconnections are brought into contact with said conductor; a secondmicrowave laminate layer with a first side and a second side, the secondlaminate layer being fixed to the first laminate layer in such a waythat the second side of the second laminate layer faces at least a partof the first side of the first laminate layer; where the second laminatelayer further extends outside the outer limit of the first laminatelayer, said conductor continuing on the second side of the secondlaminate layer without contacting the first laminate layer.
 2. Themicrowave chip supporting structure according to claim 1, characterizedin that said bottom side has at least one ground connection which iselectrically connected to said ground plane.
 3. The microwave chipsupporting structure according to claim 1 wherein the second laminatelayer has a second recess, having essentially the same position as thefirst recess, but being larger, allowing the chip connections to bebrought into contact with said conductor by means of bond wires.
 4. Themicrowave chip supporting structure according to claim 3, wherein thesecond recess is filled with a protective filler substance.
 5. Themicrowave chip supporting structure according to claim 3 wherein a coveris placed on the first side of the second laminate layer, covering thechip.
 6. The microwave chip supporting structure according to claim 1,wherein the second laminate layer covers the microwave chip, carryingthe conductors partly into the first recess, enabling them to achieve adirect contact with the chip connections.
 7. The microwave chipsupporting structure according to claim 1 wherein the first laminatelayer carries the conductors partly into the first recess, enabling themto achieve a direct contact with the chip connections.
 8. The microwavechip supporting structure according to claim 1, wherein the secondlaminate layer has a recess arranged to receive a microwave chip, themicrowave chip having a top side and a bottom side, where the chip isarranged to rest on the first side of the first laminate layer in such away that connections on the bottom side of the chip are brought intocontact with the conductor formed on the first side of the firstlaminate layer.
 9. The microwave chip supporting structure according toclaim 8, wherein the connections between conductors and the chipconnections are in the form of ball connectors.
 10. The microwave chipsupporting structure according to claim 8, wherein the recess is filledwith a protective filler substance.
 11. The microwave chip supportingstructure according to claim 8, wherein a cover is placed on the firstside of the second laminate layer covering the microwave chip.
 12. Themicrowave chip supporting structure according to claim 1, arranged forbeing placed in a recess, formed in a first Printed Circuit Board (PCB),the first PCB being attached to a second PCB in such a way that a secondside of the first PCB and a first side of the second PCB face each otherwith a PCB ground plane positioned between the second side of the firstPCB and the first side of the second PCB.
 13. The microwave chipsupporting structure according to claim 12, wherein a part of the PCBground plane is forming an accessible surface via the recess, againstwhich the supporting structure may be fixed.
 14. The microwave chipsupporting structure according to claim 12, wherein the first PCB has athickness that essentially is the same as the thickness of the firstlaminate layer, resulting in that said conductor, when carried only bythe second laminate layer, will rest on corresponding PCB conductors onthe first PCB, enabling an electrical connection between said conductoron the second laminate and the PCB conductors.
 15. The microwave chipsupporting structure according to claim 12, wherein the PCB conductorsare in the form of a Co-Planar Waveguide.